Method of sizing paper with fatty acid condensation products



United States Patent 3,404,064 METHOD OF SIZING PAPER WITH FATTY ACID CONDENSATION PRODUCTS Charles E. Feazel, Mountain Brook, Ala., assignor to Allied Chemical Corporation, New York, N.Y., a corporation of New York No Drawing. Continuation-impart of application Ser. No. 299,157, Aug. 1, 1963. This application May 12, 1967, Ser. No. 637,933

1 Claim. (Cl. 162179) ABSTRACT OF THE DISCLOSURE This application relates to a method of internally sizing paper by mixing with an aqueous slurry of paper pulp 0.2 to 2.5% by weight, based on the weight of the dry pulp, of a condensation product obtained by heating, in the presence of a catalyst, at least one fatty acid of the formula RCOOH, wherein R is an unsubstituted long chain hydrocarbon radical containing 9 to 25 carbon atoms, the condensation product being further characterized by at least 32 percent by weight of unsaponifiable matter and by having a mean molecular weight of at least 3 times that of said acid, and then forming the thus treated paper pulp into sheets. Preferably the fatty acid starting material contains at least about 40% C2042 saturated acids and the resultant condensation product is treated with alkali and has its Water soluble fraction removed before mixing with the slurry.

This application is a continuation-in-part Of U.S. Ser. No. 299,157, filed Aug. 1, 1963, now abandoned.

This invention relates to the manufacture of paper and more particularly to a new and improved method of paper SlZlIlg.

Current procedures for paper sizing involve two distinct principal methods: 1) internal sizing wherein the sizing agent is mixed with the fiber furnish and thereafter the entire mass is formed into a sheet having a uniform distribution of fibers and sizing agent, and (2) surface sizing which involves the application of a sizing agent to the surface of an already formed paper. This invention is particularly concerned with the internal sizing pro cedure.

Rosin size, which consists mainly of a body of abietic acid, is currently the most widely employed sizing agent for the internal sizing of paper. An aqueous solution of the sodium salt of this body, obtained by dissolving rosin in a solution of an alkali, customarily is added to paper pulp with agitation; and, by treatment with a soluble aluminum salt, the rosin size is precipitated and deposited upon the fibers. Although rosin size is currently the most widely used type of paper size, it nevertheless possesses certain undesirable characteristics. More specifically, rosin size in the paper tends to lower the brightness of the paper as well as the burst, tensile, tearing and particularly the folding strength. Furthermore, paper which has been sized with a rosin size tends to lose strength on aging. In addition, it is very difiicult to satisfactorily size paper with rosin size under alkaline conditions, a very undesirable characteristic, since there is a need for paper sizes which are effective in the presence of alkaline fillers. Moreover, it is known that the strength and aging stability of papers are adversely affected by low pH conditions so that in many instances, paper sizing at a pH value higher than that normally used for rosin sizing is very desirable.

More recently, ketene dimers have been suggested as sizing agents. These ketene dimers are added to the paper pulp to convert the hydroxyl groups of the fibers to hydrophobic groups which repel water. Although the use of ketene dimers as paper sizing agents in the internal size ice procedure reduces some of the undesirable characteristics of rosin sizing, unfortunately new problems are created. For example, paper sizing with ketene dimers is inefi'ective in the presence of alum and therefore presents a serious deterrent to its use since most papermill systems in operation today employ alum. Furthermore, sizing cannot be obtained with ketene dimers on reworked papers since the majority of these reworked papers contain residual alum from prior sizing processes. A further disadvantage of ketene dimer sizing is that the retention of the ketene dimer is poor when it is added at the wet end of the process, and consequently, costly additives must be employed to increase the retention of the ketene dimer by the fibers.

An object of the present invention is to provide an eflicient economical method for the internal sizing of paper. Another object of the invention is to provide new sizing agents for internal sizing of paper. A further object of the invention is to provide an improved paper product. Other objects and advantages will become apparent from the following description.

In accordance with the present invention, internal sizing of paper is effected by dispersing the condensation product of an acid compound having the formula RCOOH wherein R is an unsubstituted long chain hydrocarbon radical, said condensation product being furthencharacterized by at least 32% by weight of unsaponifiable matter and having a mean molecular weight of at least three times that of said acid, in an aqueous slurry of paper pulp and adding a precipitating agent to precipitate and deposit the sizing agent onto the fibers of the pulp. The treated pulp may then be formed into sheets or webs in the conventional manner, which normally includes drying by the application of heat. Although some degree of sizing is present in the paper after it is formed and dried it has been found that a drastic improvement in the paper size is effected by aging the paper after forming for a period of from about 1 to about 7 days, preferably from about 1 to about 2 days.

The sizing agents of the present invention may be produced according to the process described in U.S.P. 2,923,718. As disclosed in U.S. Patent 2,923,718, column 1, lines 6972, it is preferred that R in the above formula is an alkyl group having a chain length of from 9 to 25 carbon atoms. As further disclosed by that patent, the sizing agent of the present invention can be obtained by condensing fatty acids in the presence of a catalyst selected from the group consisting of boric acid, boric oxide, ammonium pentaborate, trimethyl borate, triethyl borate, mannitol borate, and the mixed anhydrides of boric acid and fatty acid. The sizing agents may also be prepared by condensing at least one fatty acid in the presence of BF They are characterized by a substantial amount, preferably at least 32%, of unsaponifiable matter, a low acid and saponification value, an increased iodine value as compared to the starting material and a high mean molecular weight. A mean molecular weight of the unsaponifiable portion is roughly in accordance with or higher than the calculated molecular weight of a theoretical condensation product of 3 molecules of fatty acid. They have a molecular structure which contains at least 3 alkyl chains. Examples of fatty acids useful as starting materials in the preparation of the fatty acid condensation products of the present invention are oleic, stearic and linoleic acid.

The preferred condensation products used in the process of this invention have been found to be those prepared from acid compositions of the type described above wherein at least about 40% of the acids are saturated C -C acids. An example of such an acid composition is Industrene 4022, a mixture of saturated fatty acids derived from fish oil by hydrogenation and saponification, sold by Humko Products Division, National Dairy Products Corporation. It has been found that condensation products prepared from acids of this type achieve acceptable paper sizing'when applied in reduced concentrations from those required when using condensation products of shorter chain fatty acids. Condensation products made from saturated acids have been found to be more suitable than unsaturated acids. Furthermore, it has been found that aging requirements of the formed paper can be substantially reduced by treating these preferred condensation products with hot alkali and removing the water soluble fraction produced thereby before applying the condensation product to the paper pulp.

vT he new sizing agents when used in the internal paper sizing procedure produce a sized paper having superior qualities over rosin-sized paper with regard to brightness, tensile strength and folding strength. Moreover, the sizing can be effected under alkaline conditions and can therefore be employed in those cases where alkaline fillers are added to the paper pulp.

Basically, internal sizing is accomplished by dispersing an emulsion of a fatty acid condensation product as hereinbefore described in an aqueous paper pulp slurry and depositing the product on the pulp. An agent such as alum may be used to facilitate the deposition. The pulp, internally sized with the fatty acid condensation product is thereafter formed into a sheet in a manner conventional in the paper industry.

The fatty acid condensation products are obtained by condensing at least one fatty acid in the presence of an oxygen-containing boron compound, for example, condensing oleic acid in the presence of boric acid. Fatty acid condensation products useful in the present invention may also be produced by condensing a fatty acid in presence of BP etherate. Since the fatty acid condensation products are substantially insoluble in water, they are preferably applied as emulsions in order to provide an even distribution of sizing agent on the fiber of the pulp. A convenient procedure is to apply the fatty acid condensation product in the form of an aqueous emulsion which is obtained by adding an emulsifying agent and organic thickening agent, such as a cationic starch to an aqueous dispersion of the condensation product and to add this emulsion with sufiicient agitation and stirring to the aqueous paper pulp slurry. The procedure for preparing the emulsion and depositing the size on the fiber is a matter of convenience and may be accomplished by any of the methods known in the art. For example the emulsion may be prepared by mixing the fatty acid condensation product with a soap, an emulsifying agent, or, preferably, a cationic starch, or mixtures of these, to form a suitable emulsion of the fatty acid condensation product. Examples of suitable emulsifying agents are polyoxyethylene sorbitan ethers and carboxymethylcellulose. An example of a suitable starch useful in the preparation of suitable emulsions is Cato 8 a product of National Starch Company. The use of starch is advantageous not only as an aid for dispersing the fatty acid condensation product but also because it aids in retaining the sizing agent on the fiber.

The pH value prior to the addition of sizing and precipitating agent may be varied over a wide range from about pH to pH 10. The pH of the pulp slurry may be conveniently adjusted to within the range of 8 to 10 by the addition of alkaline mediums such as dilute solutions of sodium carbonate or sodium hydroxide. Since the sizing is effective in the presence of alkaline mediums, the paper may be advantageously sized in the presence of alkaline fillers without a decrease of the folding strength or loss of water absorption qualities of the sized paper.

In one embodiment of my novel method a condensation product is prepared according to the method disclosed in US. Patent 2,923,718, using as a starting material oleic or stearic acid. In accordance with this method oleic acid Cit is heated to a temperature of about 220 to 290 C. for about 6 hours in the presence of a boric acid catalyst. The product is thereafter freed of unreacted acid by dissolving it in benzene, extracting the solution with aqueous sodium carbonate, then washing the benzene solution with water. The crude product which forms a red-brown viscous oil having an iodine number of around 117 and a saponification number of about 112, is insoluble in water and is therefore preferably applied to the pulp in the form of an emulsion to induce uniform distribution onto the fibers of the pulp. The emulsion is prepared by mixing the product with an emulsifying agent or a cationic starch such as Cato 8, and this emulsion is then added to the paper pulp slurry, for example in the beater of a papermaking system. The mixture is then agitated to thoroughly mix the two masses. The amount of oleic acid condensation product applied to the pulp may be varied dependent upon the requirements of the sized paper. Results superior to rosin sizing are obtained at concentrations of oleic condensation product lower than required for similar sizing with rosin sizes. Comparative analysis has indicated that as low as 1% oleic sizing agent based on bone dry pulp is as effective as 2.5% concentration of a superior grade of rosin size. With this concentration of oleic acid condensation product, that is 1%, it is noted that the sized paper had better aging stability than could be achieved by rosin sizing. In addition, it was noted, surprisingly so, that in some instances the folding strength of the paper was improved remarkably by sizing with the condensation products of the present invention even before heat treating the paper. This effect is very unusual, considering the decrease in folding endurance that usually accompanies rosin sizing. As a matter of fact, experimentation has shown that under some conditions the folding endurance of aged specimens sized with the sizing agents present in the invention is approximately twice that of the unaged paper.

In the preferred embodiment of my novel method a condensation product can be prepared in a manner substantially the same as that described above, for example, by heating Industrene 4022 starting material gradually at reduced pressure to a temperature of about 300 C. over about a 48-hour period with a boric acid catalyst and extracting the product with boiling alcohol. The resulting alcohol-insoluble condensate has an acid number of about 3 and a saponification number of about 10. It is insoluble in water and is therefore preferably applied to paper pulp in the form of an emulsion, which can be prepared and applied in the manner described in the previous paragraph. Good sizing can be obtained by the use of as low as 0.5% of this preferred condensation product based on the weight of the bone dry pulp.

The preferred condensation products of this invention have been found to function particularly well as sizing agents when they are treated with alkali and the resulting water soluble fraction is removed before the condensation product is emulsified and applied to the paper pulp. This alkali treatment can be effected, for example, by refluxing the condensation product for several hours with about 0.1 its weight of sodium hydroxide in about its weight of benzene and about twice its weight of alcohol and then washing the resultant solid residue with hot water to remove the water soluble fraction.

Generally, the sizing efficiency of the treated paper may be determined in a variety of ways. A particularly suitable procedure and one which has received considerable attention in the paper sizing industry is the Cobb size test, procedure T441 of the Technical Association of the Pulp and Paper Industry (TAPPI). In this procedure, an area of the sheet is defined by clamping it under a metal ring 10 cm. in inside diameter, and then the ring is filled with water. After a measured interval of time, usually 1 to 5 minutes, the Water is poured off, the ring is removed, and the paper is blotted to remove surface water. The amount of water absorbed is determined from the weights of the paper before and after the exposure, and the Cobb size value is calculated and reported as grams of water absorbed per square meter of paper. The lower the Cobb value, the better the sizing. For a 3 minute exposure time a value of 50 g./m. or lower indicates good sizing. For a 1 minute exposure time a value of 30 g./m. or lower indicates good sizing.

The following examples illustrate the invention.

EXAMPLE 1 The following example shows the sizing efficiency of the oleic acid condensation product of the present invention.

Handsheets containing 1% sizing agent were prepared as follows:

A slurry was prepared by tearing into small pieces 4.0 grams of 60-brightness pulp which was then placed into a Waring Blendor with 400 ml. of distilled water. The mixture was agitated for 2 minutes and the pH was adjusted in the range of 8-10. Thereafter, an emulsion of the oleic acid condensation product was added to give 1% based on the weight of the pulp and agitation was continued for an additional one minute. The action of the Waring Blendor was sufficient for complete distintegration of the pulp sheets and the attainment of a Canadian Standard freeness value of 750 for the pulp.

Handsheets were formed in a Williamson 8" x 8" sheet mold with a ISO-mesh stainless steel screen. For each handsheet, the slurry of the mixed pulp was poured into the sheet mold; diluted to 5 liters; and the water was drained off to form a sheet. The sheet was removed from the screen on a blotter, pressed between blotters for 1 to 2 minutes at 100 p.s.i., and then dried on an electric dryer at 150 C. The sizing efficiency was determined by the Cobb size test according to TAPPI procedure T441, and the results are tabulated in Table I.

TABLE I Size Oleic acid condensation product.

Method of application Size emulsion with starch.

Cobb size (1% size) 32.

1 For 3 minute penetration time.

EXAMPLE 2 Size Oleic acid condensation product. Method of application Size emulsion with starch,

precipitated with alum. Cobb size (0.2% size) 45.

1 For 1 minute penetration time.

EXAMPLE 3 The following example shows the sizing efficiency of a stearic acid condensation product of the present invention.

Handsheets containing 2.5% stearic acid condensation product were prepared according to the procedure described in Example 1. The sizing efficiency was deter mined by the Cobb size test according to TAPPI procedure T441, and the results are indicated below.

Size Stearic acid condensation product.

Method of application Size emulsion with starch,

precipitated with alum.

6 Cobb size (2.5% size):

For 1 minute penetration time 19. For 3 minutes penetration time 20.

EXAMPLE 4 The following example shows the effects of prolonged aging on sizing and on the strength of paper sized with an oleic acid condensation product. The paper specimens prepared according to Example 2 were heat aged according to TAPPI procedure T453-M48, by heating for 72 hours at C. This accelerated aging is generally considered to be equivalent to about 25 years of normal aging. According to the information given with the TAPPI procedure, the property of the paper that is most affected by aging is the brittleness; therefore, the aged papers were evaluated by measurements of folding endurance. Cobb size measurements were also made on aged and unaged papers. Five measurements of Cob-b size values and of folding endurance were made on each sample. The average results from the measurements on aged and unaged paper specimens are shown in the table below.

SizeOleic acid condensation product percent 1.0 Cobb size (1 min):

Before aging 33 After aging 17 Folds to break:

Before aging 844 After aging 1662 EXAMPLE 5 This example shows the retention qualities of the oleic acid condensation product by the paper.

One set of five handsheets was sized with a starch emulsion of the oleic acid product. A quantity of the emulsion containing 0.2% of the size (based on pulp) was added to the pulp, and was precipitated with an equal quantity of alum.

Cobb size measurements were made on the handsheets. Then the sheets were extracted with benzene for 24 hours in a Soxhlet extractor. After drying and reconditioning at 72 F. and 50% RH, Cobb size measurements were repeated.

Results from the experiment indicated below show that the sizing quality of the oleic acid product was not adversely affected by extraction.

Retention of sizes by paper handsheets 1 Size Oleic acid product. Unextracted (Cobb size, 1 min.) 45. Extracted (Cobb size, 1 min.) 36.

Tl1e haudsheet was treated with 0.2% of the oleic acid product.

Extracted 24 hours with benzene.

EXAMPLE 6 This example shows the sizing efficiency of the Industrene 4022 condensation product which is exemplary of the preferred condensation products of the present invention.

The procedure of Example 1 was substantially repeated except that the condensation product used was that identified in the previous paragraph and it was present in the amount of 0.5% based on the dry weight of the pulp. The results are as indicated below:

Size Industrene 4022 condensation product. Method of application Size emulsion with starch.

Cobb size 1 (0.5% size) 42.

For 3 minute penetration time.

7 EXAMPLE 7 This example shows the sizing efficiency of alkali treated Industrene 4022 condensation product which is exemplary of the particularly useful sizes obtained by alkali treatment of the preferred condensation products of the present invention.

The procedure of Example 1 was substantially re peated except that the condensation product used was that identified in the previous paragraph and it was present in the amount of 0.5% based on the dry weight of the pulp. The results are as indicated below:

Size Alkali treated Industrene 4022 condensation product.

Method of application Size emulsion with starch.

Cobb size (0.5% size) 37.

1 For 3 minute penetration time.

Handsheets sized with alkali treated Industrene 4022 condensate showed an average folding endurance of 1871 folds to break.

Although certain preferred embodiments of the invention have been disclosed for purposes of illustration, it will be evident that various changes and modifications may be made therein without departing from the scope and spirit of the invention.

I claim:

1. A process for the internal sizing of paper which consists of forming an aqueous slurry of paper pulp having a pH within the range of about 5-10, admixing with the aqueous slurry of pulp an emulsion of the condensation product obtained by heating in the presence of a catalyst selected from the group consisting of boron trifluoride,

boric acid, boric oxide, ammonium pentaborate, trimethyl borate, triethyl borate, mannitol borate, and

the mixed anhydrides of boric acid and fatty acid, a mixture of fatty acids of the formula RCOOI-I comprising at least about 40% saturated fatty acids having C C chain lengths and treating the resultant condensation product with alkali and removing the watersoluble fraction therefrom,

said condensation product being further characterized by at least 32% by weight of unsaponifiable matter and by having a mean molecular weight of at least 3 times that of said acid, the amount of condensation product admixed being from about 0.5 to about 2.5% by weight based on the dry Weight of the pulp, and then forming the thus treated paper pulp into sheets having improved folding endurance.

References Cited UNITED STATES PATENTS 2,923,718 2/1960 Donatus 260407 3,008,868 11/1961 Feigley et a1. l62l79 3,097,220 7/1963 Barrett et al. 260-407 S. LEON BASHORE, Primary Examiner. 

